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Date: Wed, 19 Sep 2012 17:34:58 +0100
Subject: Re: subprocess call is not waiting.
From: andrea crotti <andrea.crotti.0@gmail.com>
To: Hans Mulder <hansmu@xs4all.nl>
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Xref: csiph.com comp.lang.python:29506

2012/9/19 Hans Mulder <hansmu@xs4all.nl>:
> Yes: using "top" is an observation problem.
>
> "Top", as the name suggests, shows only the most active processes.

Sure but "ls -lR /" is a very active process if you try to run it..
Anyway as written below I don't need this anymore.

>
> It's quite possible that your 'ls' process is not active, because
> it's waiting for your Python process to read some data from the pipe.
>
> Try using "ps" instead.  Look in thte man page for the correct
> options (they differ between platforms).  The default options do
> not show all processes, so they may not show the process you're
> looking for.
>
>> Anyway I also need to know when the process is over while waiting, so
>> probably a thread is the only way..
>
> This sounds confused.
>
> You don't need threads.  When 'ls' finishes, you'll read end-of-file
> on the proc.stdout pipe.  You should then call proc.wait() to reap
> its exit status (if you don't, you'll leave a zombie process).
> Since the process has already finished, the proc.wait() call will
> not actually do any waiting.
>
>
> Hope this helps,
>


Well there is a process which has to do two things, monitor
periodically some external conditions (filesystem / db), and launch a
process that can take very long time.

So I can't put a wait anywhere, or I'll stop everything else.  But at
the same time I need to know when the process is finished, which I
could do but without a wait might get hacky.

So I'm quite sure I just need to run the subprocess in a subthread
unless I'm missing something obvious..